Explosive device



Aug. 24, 1954 H. w. BOTTS EXPLOSIVE DEVICE Filed Sept. 23, 1949 FIG.|

FIG.5

HENRY w. BOTTS I 7 INVENTOR.

AGENT.

Patented Aug. 24, 1954 EXPLOSIVE DEVICE Henry W. Botts, Carthage, Mo., assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware Application September 23, 1949, Serial No. 117,352

9 Claims.

This invention relates generally to container units which may be joined together with similar units to form a column and more particularly to an explosive device comprising such units which may be joined together with similar explosive devices to form an explosive column.

In U. S. Patent 2,317,354 to Bennett there is disclosed an explosive cartridge assembly comprising a plurality of explosive cartridges connected in end-to-end abutting relationship by a plurality of connecting sleeves which threadedly engage the cartridges. With such an assembly, the cartridges and sleeves are supplied in a standard unit which may be readily built up in the field by simply screwing the units together to form an explosive column of the length desired. Such explosive assemblies have found wide use in geophysical prospecting and as geophysical prospecting techniques have advanced, explosive columns of increasingly greater length have been employed. As a result the amount of tensile stress on the entire column, which stress is translated into torsional force due to the pitch of the threaded sleeves and cartridges, has been correspondingly increased. The resultant effect of this increased torsional force in a tendency for a section of the explosive column to rotate. This rotation is highly undesirable since even a slight rotation will cause a corresponding gap between the ends of the explosive cartridges disposed at the point where rotation occurs. Depending on the type of explosive which is being employed, a substantial gap can result in incomplete propagation, or if its width becomes great enough, a total failure of propagation. Furthermore, if the weight of the explosive column is still further increased, the cartridge and sleeve having the least frictional resistance in threaded relationship actually can unspiral to the degree that disengagement takes place and the portion of the assembly therebelow may be dropped during lowering of the column into a vertical borehole.

In U. S. Patent 2,403,488 to Bennett there is disclosed a threaded explosive assembly composed of threaded cartridges and threaded sleeves provided with an additional friction thread on each cartridge in frictional engagement with its respective sleeve. This friction thread permits screwing of the sleeves upon the cartridges to form an explosive assembly and assists in the prevention of the sections of the assembly from becoming unscrewed as a result of the torsional forces created by the weight of a vertically suspended assembly or column. The use of such a friction thread does raise the permissible limit of the over-all weight of such a threaded explosive assembly and is thus a valuable improvement over the assembly of U. S. 2,317,354. However, as the lengths of the columns used in geophysical prospecting have increased still further, even this improved assembly will unspiral as a result of the torsional force created by the weight of the vertically suspended column. The answer to this problem cannot be found in increasing the size of the friction thread to effect a corresponding resistance to the resultant torsional force, since a point is reached Where it becomes too difficult or impossible to assemble the cartridges and sleeves to form the column.

The object of the present invention, therefore, is a container unit which is adapted to be threadedly connected with similar container units to form a column which will not unspiral or otherwise disengage as a result of tensile stress to which the column may be subjected in any practical application.

The further object of the present invention is an explosive device which is adapted to be threadedly connected with similar explosive devices to form a column which will not unspiral or otherwise disengage as a result of tensile stress to which the column may be subjected in any practical application.

Generally described the present invention is a device adapted to be connected together with similar devices to form a column which in combination comprises an outer, internally threaded tubular sleeve and an inner, externally threaded tubular member of lesser diameter threadedly disposed within the outer sleeve by engagement of male and female threads, one set of threads having at least one beveled edge with a slope of between about 6 and about 30 to the longitudinal axis of the device to receive the other set of threads in looking relationship when tensile stress occurs between said outer sleeve and inner tubular member. A further embodiment of the invention is a threaded assembly having a plurality of externally threaded tubular members held in substantially end-to-end abutting relationship by at least one internally threaded sleeve, one set of threads in the assembly having at least one beveled edge with a slope of between about 6 and about 30 to the longitudinal axis of the assembly; said beveled edge receiving the other set of threads in locked relationship. In the preferred embodiments which constitute the particular object of the invention, the inner tubular member is an externally threaded explosive cartridge.

Although it is preferred that the female thread of the devices or assemblies of the invention carry the beveled edge or edges, the edge or edges of either the male or female thread may be beveled. While the female thread may be carried by either the sleeve or the inner tubular member, it is preferred that the female thread be carried by the sleeve.

Having generally described the invention, various embodiments thereof will be described in greater detail with reference to the accompanying drawing. Fig. 1 represents an elevational view of a threaded cartridge and sleeve. Fig. 2 is a fragmentary, sectional view taken on line 2-2 of Fig. 1, illustrating in detail an application of the invention with cartridge and sleeve engaged by a male thread carried by the cartridge, and a female thread carried by the sleeve. Fig. 3 is an elevational view of an explosive assembly in accordance with the invention. Fig. 4 is a fragmentary, sectional View illustrating in detail an embodiment of the invention with cartridge and sleeve engaged by a female thread carried by the cartridge, and a male thread carried by the sleeve. Figs. 5 and 6 are side views of a strip of material used to form the female thread on either cartridge or sleeve and show two of the various types of operable beveled edges. Fig. '7 is an elevational view of a further embodiment of the explosive assembly in accordance with the inven-- tion.

Referring now to the Figs. 1, 2 and 3, an explosive cartridge I is provided with a wrapper 2 which has an external spirally disposed male thread 3 throughout its length. The cartridge I threadedly engages tubular sleeve :I which is substantially the same length as the cartridge. The sleeve iis provided with an internal longitudinaliy continuous female thread 5 which is a groove defined by a strip of cellulosic material spirally disposed about the inner periphery of the sleeve 4 in spaced relationship. The female thread 5 has beveled edges 8 which receive the male thread 3 in locking relationship when tensile stress occurs between cartridge and sleeve.

With particular reference to Fig. 2 the sleeve 4 comprises an outer wrapping it adhesively affixed to an inner wrapping 8 which has been wrapped in spaced relationship to form the female thread 5. The edges of the inner wrapping 8 are beveled to form the beveled edges 5 of the female thread 5. The cartridge wrapper 2 comprises an outer wrapping 9 which covers the cord l0, said wrapping 9 and cord H} forming the male thread 3. The wrapping 9 is adhesively aflixed to an inner wrapper I I which is adjacent to the explosive I2.

Referring particularly to Fig. 3, the male threaded cartridges I, as shown in Fig. 1 and Fig. 2, are threadedly engaged with female threaded sleeves 4, as shown in Figs. 1 and 2, to form an 4 explosive column. The cartridges I are disposed in end-to-end abutting relationship within sleeves d which are also in end-to-end abutting relationship. The sleeves 4 are substantially the same length as the cartridges I.

In Fig. 4 is shown a fragmentary section of a cartridge 40 having a wrapper comprising an inner wrapping 4| and an outer wrapping 42. Outer wrapping 42 is spirally disposed and adhesively afiixed about inner wrapping 4| in spaced relationship to form a female thread 43, having beveled edges M throughout the length of the cartridge. The cartridge 49' is disposed within a sleeve 45 comprising an outer wrapper 46 and an inner wrapper 41 adhesively affixed thereto. Cord 42 is spirally disposed throughout the length of the sleeve beneath the inner Wrapper 4'. and, with inner wrapper 41, forms a male thread 49 throughout the length of the sleeve.

In Fig. 5 is shown a side view of a strip 50 of chipboard having fully beveled edges 5| while in Fig. 6 is shown a side view of a similar strip 60 of chipboard having half-beveled edges 6 I.

In Fig. 7, male threaded cartridges I are disposed and maintained in end-to-end propagating relationship by female threaded sleeves ID. The female thread of the sleeves III is formed from beveled chipboard spirally disposed about the inner periphery of the sleeves in spaced relationship. However, the sleeves IB are substantially shorter than the cartridges I and are not in endto-end abutting relationship as in the column shown in Fig. 3.

Explosive columns in accordance with the invention are easily assembled. The sleeve and cartridges are preferably stored, transported and supplied to the field as integral, threadedly engaged units of one sleeve and one cartridge. In forming either the column of Fig. 3 or that of Fig. '7, the cartridges are partially unscrewed from their respective sleeves until the cartridge is threadedly engaged with approximately half of the length of the sleeve. The extending end of the cartridge of one unit is then screwed into the open end of the sleeve of a second unit until the ends of the cartridges are in end-to-end abutting relationship. Additional torsional force is then applied until the male thread is forced upon the bevel of the female thread in tight, locking relationship. Additional units may now be threadedly engaged in this same manner until a column of the desired length is obtained. If the sleeves are substantially the same length as the cartridges as shown in Fig. 3, the sleeves will be in end-to-end abutting relationship as well as the cartridges. If the sleeves are substantially shorter than the cartridges as shown in Fig. '7, the ends of the sleeves will not abut.

If the cartridges and sleeves are supplied separately, they may be threadedly engaged in units of one sleeve and one cartridge and the column built up as above described. Alternatively, the column may be built up of separate components by alternately engaging separate sleeves and cartridge from either or both ends of the starting sleeve or cartridge and applying the torsional force necessary to cause the male threads to mount the beveled edge of the female thread and form the desired locking relationship.

Of the assemblies hereinabove described, the assembly according to Fig. 3 is naturally the stronger of the two and is preferred for heavier columns, especially if cartridges of large diameter are to be employed. Moreover, the smooth exterior of an assembly such as that shown in Fig. 3 makes it somewhat easier to charge the column into a borehole than in the case with the assembly shown in Fig. 7. However, where columns of less weight are to be assembled and especially where cartridges of smaller diameter are to be employed, the assembly of Fig. 7 is preferred for reasons of economy unless the roughness caused by the edges of the noncontiguous sleeves is undesirable in the particular application.

While it is unnecessary to lock each cartridge and sleeve together while assembling the column, such procedure is preferred in order to insure a minimum of separation between the cartridges in the column when suspended. If desired, however, the cartridges and sleeves need only be screwed together until the ends of the cartridges abut. Then when the column is suspended, the beveled edge of one set of threads engages the other set of threads in locking relationship due to the resultant tensile stress.

Although from the practical standpoint it is preferred that the female thread have both its edges beveled in accordance with the invention, the male thread enters into locking relationship with only one beveled edge of the female thread at one time. If the female thread is carried by the sleeve, and the male thread by the cartridge, the male thread enters into locking relationship with the beveled edge nearest the end of the sleeve into which the cartridge is inserted. Conversely, if the female thread is carried by the cartridge and the male thread by the sleeve, the male thread enters into locking relationship with the beveled edge nearest the midpoint of the cartridge. Consequently, if it is desired to bevel only one edge of the female thread, the bevel must be formed on opposite edges of the thread on either side of the midopint of the sleeve or cartridge. If the female thread is carried by the sleeve, then the single beveled edge in each half of the sleeve must be the edge of the thread nearest that end of the sleeve. If the female thread is carried by the cartridge, then the single beveled edge in each half of the cartridge must be the edge of the thread nearest the midpoint of the cartridge. As a result, in the assembled unit or column, in accordance with the invention, the single beveled edge will always be on the edge of the female thread nearest the adjacent sleeve end, whether the female thread is carried by sleeve or cartridge. It is apparent, therefore, that if only a single beveled edge is employed, the cellulosic material forming the thread must be processed very carefully to insure that the bevel is on the proper edge in each half of the sleeve or cartridge. Furthermore, for optimum locking efficiency, the two cartridges joined together must abut at the midopint of the sleeve when the single beveled edge is employed.

It is also within the purview of the invention that the beveled edge or edges be formed on the male thread rather than on the female thread. If desired, the male thread may be formed by a strip-of chipboard or other suitable material, the edge or edges of the strip being beveled to engage the unbeveled edge of the female thread in locking relationship when tensile stress occurs. The preferred beveled male thread is formed from a rectangular strip of chipboard having one or both edges beveled as hereinabove described relative to the female thread. This strip is then spirally woundabout the cartridge or inner periphery of the sleeve in the same 6 Y manner as the cord normally used. Accordin to this embodiment of the invention, the female thread is formed with the normal vertical edges. The vertical edge of the female thread then enters into locking relationship with the beveled edge of the male thread when tensile stress occurs between cartridge and sleeve. If desired, the beveled male thread may also be covered with a layer of paper as in the case of the normal male thread formed from a cord. As long as the beveled surface is not altered, a covering layer of glued paper enhances the strength of the thread.

The preferred method of manufacturing the cartridge wrappers and sleeves of the present invention is by spiral winding. This method of manufacture is economical and permits formation of the necessary threads on the sleeves and cartridge wrappers in a facile manner, since these threads unwind on the respective parts at the same pitch used for the spiral winding. However, this method of manufacture requires the use of strip, flat materal, such as paper or other cellulosic material. Materials of this kind have a considerable range of dimensional stability. Moreover, spiral wrapping machines and convolution wrapping machines, particularly when adhesives are employed, are incapable of manufacturing paper or other cellulosic tubes within close tolerances. The range of dimensional stability inherent in cellulosic material, plus the best tolerance limit obtainable in machines of the class described, does not permit a really close fit between the sleeve thread and the cartridge thread, male or female as the case may be. When a close fit is attempted, it is impossible, in a large percentage of cases, to manually screw the cartridges and sleeves together. As a result of this fact it has been found necessary to provide a relatively loose fit between the sleeve thread and the cartridge thread. This relatively loose fit naturally has a low factor of frictional resistance and if the female thread does not have a beveled edge in accordance with the present invention, the weight of a substantial column will cause a variable amount of disengagement as hereinabove described. By forming the female thread with a beveled edge or with beveled edges, however, it is possible to manufacture the sleeves and cartridges without attempting to obtain close tolerances and still be assured that an explosive column built up from the sleeves and cartridges will be an integral assembly with the cartridges maintained in propagating relationship.

Cellulosic materials are the preferred materials of construction for the internal tubular members or the cartridge shells. Similarly, a cellulosic twine such as paper, hemp, jute, or cotton twine is preferred as the cord material for forming the male threads. For cartridges from about 2 to about 4 inches in diameter and from about 12 to 30 inches in length, it has been found that a cord about 0.065 in. in diameter, covered with an outer Wrapping of manila paper in the order of a 68 /2 lb. paper will result in a cartridge thread sufficiently strong to withstand any load practically imposed on columns built up of cartridges such as those described. However, paper weights and cord sizes other than these preferred types are operable. For optimum results, the diameter of the cord forming the male thread and the slope of the beveled edge of the female thread must be properly coordinated. The cords diameter must not be so great, for a particular slope, that the male thread is unable to climb sufficiently far up the beveled edge to form the desired friction lock between sleeve and cartridge. In like manner the diameter of the cord should not be so small for a particular female thread that an adequate friction lock cannot be obtained between the cord and the beveled edge. If it is desired that the cartridge carry a female thread instead of a male thread, it is preferred that chipboard or equivalent material be used as the outer wrapping. The edges of the chipboard or other material are preferably beveled to the desired amount by any suitable means prior to use.

It has been found that to be satisfactory in the invention, the slope of the beveled edge of the male or female thread should be between about 6 and about 30 to the longitudinal axis of the sleeve or cartridge 01' to the longitudinal axis of the column formed therefrom. If the beveled edge has a slope of less than 6, it has been found that the cartridges and sleeves often become unintentionally locked together when screwing them together and when backing the sleeve off onehalf way in the field when integral units of a cartridge within a sleeve are furnished. Furthermore, it has been found that with a slope of less than 6, undesirable separation is often obtained between cartridges of a suspended column. This is due to the fact that with a bevel of less than about 6", it is necessary to force the unbeveled thread much further up the bevel to obtain the desired locking relationship. Moreover, it has also been found that when slopes of less than 6 are employed, the cartridges are more apt to strip through the sleeves in the heavier columns. On the other hand, if the slope exceeds about 30, then the angle between the beveled edge and the outer periphery of the cartridge becomes too large to form the desired locking relationship between the bevel and the male thread. A slope of between about 9 and about 18 is preferred.

Cellulosic materials are likewise preferred as the materials of construction for both the inner and the outer wrapping of the sleeve. It is preferred to form the outer wrapping from a plurality of layers of paper. Chipboard or equivalent material is preferred as the material for the inner wrapping of the sleeve which, when wound in spaced relationship, forms the female thread 1 on the inner periphery of the sleeve. The thickness of the chipboard will depend upon the size and the weight of the cartridge to be used in conjunction with the particular sleeve. Chipboard of between 30 point and 40 point or between approximately 0.03 and 0.040 in. thick, has been found suitable, in conjunction with the male thread heretofore described, to withstand the loads imposed on explosive columns of practical length and weight and under practical conditions. If it is desired that the sleeve carry the male thread instead of the female thread, a cord or strip with beveled edge or edges, as hereinabove described, is spirally disposed about the inner peripheral surface of the sleeve. A sleeve carrying such a male thread is preferably fabricated by simultaneously running a strip of manila paper and a cord or strip of the desired weight on a suitable mandrel and then running on the outside layer or layers in the normal manner.

Although cellulosic materials are the preferred materials of construction for the components of the invention, the invention is not so restricted. The cartridges and sleeves may, if desired, be formed from metal, metal foil or combinations of metal foil and cellulosic materials. The cartridges and shells may also be made from various types of plastic or plastic sheeting. The male thread may be formed from plastic strips or cord or from soft metal wire such as aluminum or copper.

Having now described and illustrated the present invention, the following examples are given for purposes of further illustration.

Example 1 Sleeves and cartridge shells were made similar to those shown in Figs. 1, 2 and 3. The female thread, carried by the sleeves, was formed by spirally disposing and adhesively affixing a strip of 40 point chipboard about the inner periphery of the sleeves in spaced relationship. The edges of the chipboard were fully beveled as shown in Fig. 5 so that the edge of the resulting female thread went from a feather edge to a thickness of 0.040 in. with a slope of about 17 to the longitudinal axis of the sleeve. The inner diameter of the sleeve was approximately 2.34 inches and the outer diameter of the cartridge shells, exclusive of the male thread, was approximately 2.31 inches. Both sleeves and cartridges were 21 /2 inches long. The male thread on the cartridges was formed by a kraft cord 0.061 in. in diameter covered by a single layer of 64-1b. manila paper. An empty cartridge shell was screwed halfway into each end of a sleeve and turned un-- til the male thread of each cartridge shell mounted on the beveled edge of the female thread in looking engagement therewith, and the two empty shells were in tight, end-to-end abutting relationship. This column was then suspended from the extending end of one shell, and a gradually increasing amount of weight was then attached to the end of the other cartridge shell extending from the bottom of the suspended column. The cartridge shells and sleeve did not unspiral but at 103 lbs., the lower shell stripped out of the sleeve without unspiraling.

Example 2 The test of Example 1 was repeated except that in this instance the chipboard used to form the female thread within the sleeve was only half beveled as illustrated in Fig. 6. The slope of the beveled edge was still about 17 to the longitudinal axis of the sleeve. Again the weight applied to the lower end of the column was gradually increased. The cartridge shells and sleeve did not unspiral but at 106 lbs., the lower shell stripped out of the sleeve without unspiraling.

Example 3 The test of Example 1 was repeated using an ordinary sleeve in which unbeveled 40 point chipboard was used to form the female thread. The weight at the lower end of the column was gradually increased. At 23 lbs. the column began to unspiral.

Example 4 Additional tests were made in which columns were made, as in Example 1, from two empty cartridge shells carrying a male thread, and a single sleeve carrying a female thread. The male thread, unless otherwise indicated, was formed by a kraft twine 0.065 in. in diameter spirally disposed under a single outer ply of 64-lb. manila paper. The female thread was formed by spirally disposing and adhesively affixing a strip of 40 point chipboard about the inner periphery of the sleeves in spaced relationship. Both edges of the chipboard strip were fully beveled as in Fig. 5 and had a slope of about 12. The cartridge shells were 2.31 in. in outer diameter and 21 inches long. The sleeves had an inner diameter of about 2.34 inches and were also 21 in. long. Unless otherwise indicated, each shell and sleeve was passed through a paraffin spray gallery and allowed to drain and dry at an elevated temperature. In tests 1-6 and 12-15, the two shells were first screwed into a regular sleeve in which the female thread was formed by unbeveled 40 point chipboard and tested to determine the weight necessary to cause unspiraling. In most of the tests, the fit of the cartridge in the regular sleeve was classified according to the weight necessary to initiate unspiraling as follows: Loosebelow 20 lbs; average fit-20-24 lbs.; fairly tight-25-50 lbs.; tight-65-71 lbs. The sleeves and shells in the tight category could be manually assembled only with difiiculty. The shells were then screwed into one of the sleeves in accordance with the invention and, as above described, the test was repeated. The following comparative results were obtained.

(gveig ht M ausmg axi- Iest gfi fi g Unspiralmum I R It No. P ingin Weight 95 S we Regular Applied Sleeve Lbs. Lbs. 1 Fairly tight--. 26 175 Lowier shell stripped ou 2 dO 32 210 Do. 3 Average. 24 110 Columnheld. 4.. Loose 18 110 Do. 5.. Fairly tlght 28 110 Do. 6 .110 40 110 D0. 7 115 D0. 8 115 Do. 9 115 D0.

83 Unspiraled. 180 Lower shell stripped ou 12 Average 22 201 Column held. 13 Loose 16 204 Column held but support broke.

14 do 12 201 Column held. 15 Average 219 Do.

I Shell was passed through paraffin spray gallery a second time after first application had dried.

b Both shell and sleeve passed through paraflin spray gallery a second time after first application had dried.

e Sleeve was passed through paraffin spray gallery once and allowed to dry at elevated temperature. It was then dipped by hand 1J1 molten paraffin and allowed to dry at room temperature.

In tests 8, 9 and 10, the amount of paraffin forming the waterproof coating was varied to determine the effect of different amounts of the wax on the functioning of the invention. It was found in tests 8 and 9 that the spraying of a second coating on either or both the shell and sleeve had no undesirable effect if the sleeve and shell were allowed to drain and dry in a heated atmosphere. When, however, the sleeve was hand-dipped in molten parafiin as in test 10 and allowed to retain a thick coating of the wax, the effect of the beveled edge was diminished. This is believed to be due to the fact that any amount of paraffin causes the beveled edge of the chipboard to swell to some degree. Then when the bevel is also covered with a thick film of the wax, the male thread is unable to mount the bevel to a distance necessary to effect the desired lock. In addition, the wax acts as a lubricant. Consequently, when an inordinate amount of paraffin is employed, as in test 10, the effect of the beveled edge isgreatly lessened.

Use of such'an amount of paraffin or equivalent waterproofing agent is therefore to be avoided.

Example 5 During the course of each test recorded in Example 4, measurements were taken to determine the amount of separation, if any, which occurred between the ends of the two cartridge shells within the sleeve. In all cases it was found that no separation whatever occurred in any test up to a weight of 50 lbs. The amount of separation recorded in all the tests did not exceed inch. For example, in tests 12 through 15 in which the columns held under the greatest loads without unspiraling or stripping out, the following results were obtained.

Total Separation in Inches Between Cartridge Shells atg ff Test No. A

pplied,

While it would of course be desirable to have the cartridges in tight, abutting relationship at all weight levels, separations of /8 to inch are not serious. Actually most of the explosive columns employed do not exceed 50 pounds. The test columns were assembled by one man using only normal effort in screwing the cartridge shells and sleeves together. Had the one man used more torsional force or had two men assembled the columns, the weights at which no separation Example 6 Further comparative tests were made in which the cartridge shells were actually loaded with various types of explosives. The female thread of the regular sleeves was formed by unbeveled 40 point chipboard as in the preceding examples. In the sleeves made in accordance with the invention, the female thread was formed by 40 point chipboard, the edges of which were half beveled or full beveled as indicated. The diameter of the cord employed to form the male thread was 0.065 inch in all cases and the slope of the bevel in all cases was about 12. Several of the cartridges employed with regular sleeves had additional friction threads as indicated. The sleeve-cartridge fit was classified as in Example 4. The cartridge shells were made from six plies of 104-lb. manila paper and two plies of 68 lb. manila paper unless otherwise indicated. None of the columns unspiraled or stripped at the weights employed when the female thread of the sleeves employed was formed by beveled chip- 1 1 board. The results obtained are tabulated in the table below.

12 tainers of any desired length which can be'locked into an integral unit, thus eliminating the neces- Wt to Maximum Weight Classifi ation (Jaime Applied lIl Increments c Test No. of Fit in 1 3 2 Results Regular Sleeve fi Full Bevel Bevel sleegeves Chipboard Chipboard in Sleeves in Sleeves Lbs. 1 Leosie Colulijmn held. 2 0. 3 Average Do. 4.-.. do 5. .do Do. 6. Fairly tight. 7. .do 8. Fairly loose. 9.-.. Fairly tight. Do. ll 12 13 l4 15 16 17 *2... 18 b 19 Do. 20 b manila. was also employed.

In addition to the male thread a friction thread having a diameter of .016 in.

b Cartridge shells made from one ply of 68% 1b. manila and seven plies of 104 lb.

manila. also employed.

When the sleeves and cartridges are of the same or substantially the same length in the blasting column, thesleeves are contiguous to the cartridges throughout the length of the assembly with the exception that each end of the column may have extending therefrom either part of a sleeve or part of a cartridge, depending upon the distance the first cartridge is screwed into the first sleeve. If, as is shown in Fig. 7, the sleeves are much shorter than the cartridges, substantial portions of the cartridges are not enclosed in the sleeves. The length of these shorter sleeves will depend on the amount of weight they must support. The optimum length of the shorter sleeves must be determined empirically for the particular cartridge diameter and weight. In the case of the popular 2 inch cartridge normally used in geophysical prospecting, it has been found that the sleeve should preferably engage about 5 inches of each cartridge.

The chipboard or other material used to form the threads in accordance with this invention may be beveled in any suitable Way. For example, the chipboard or other material may be beveled with an ordinary grinding wheel.

The explosive units or assemblies of the inven tion may be utilized in any type of blasting worl: where a column of explosive is desired. Any type of blasting explosive such as gelatinous explosives, ammonium nitrate explosives, various types of dynamite, and black powder may constitute the cartridge charge, and the use of any of these explosive in conjunction with the present invention is contemplated regardless of their particular field of use. Furthermore, while in the specific illustration given, the popular 2%; inch cartridge (actually 2.31 in. O. D., exclusive of thread) has been used, it is to be understood that cartridges of any desired size are within the purview of this invention.

Although particular description and illustration has been given with reference to its application in the explosives field, the invention is not so limited. The individual units or assemblies may be employed in many uses. The invention is particularly useful in building up shipping con- In addition to the male thread a friction thread of .028 in. in diameter was sity of stocking containers of many different lengths. Since additional advantages and applications or the invention other than those heretofore set forth will be apparent to those skilled in the art, the invention is limited only by the scope of the appended claims.

What I claim and desire to protect by Letters Patent is:

1. A device adapted to be connected coaxially with similar devices to form a column which has in combination an outer tubular sleeve internally threaded with a high pitch spiral female thread formed from cellulosic material, and threadedly engaged therewith, an inner tubular member externally threaded with a mating high pitch spiral male thread formed from cellulosic material, said female thread having a beveled side edge with a slope of between about 6' and about 30 to receive the male thread in looking relationship when tensile stress occurs between the outer sleeve and inner tubular member.

2. A device in accordance with claim 1 in which the female thread is a groove defined by a chipboard strip disposed about the inner periphery of the tubular sleeve in spaced. relationship.

3. A device in accordance with claim 1 in Which the male thread comprises a cord spirally disposed on the inner member.

4. A device in accordance with claim 1 in which the inner tubular member comprises a paper shell filled with an explosive material.

5. A device adapted to be connected coaxially with similar devices to form a column which has in combination a tubular explosive cartridge comprising a multi-ply paper shell containing explosive material, said cartridge carrying an external, high pitch, spiral, male thread consisting of a cellulosic cord disposed beneath at least one outer ply of the shell, and threadedly engaged with the cartridge, a multi-ply paper sleeve carrying a mating internal, high pitch, spiral, female thread consisting of a strip of flat cellulosic material spirally disposed about the inner periphery of the sleeve in spaced relationship, said strip of cellulosic material having beveled side edges with a slope of between about 6 and. about 30 to receive the male thread in locking relationship when tensile stres occurs between sleeve and cartridge.

6. A threaded. assembly having in combination a plurality of paper tubes carrying an external, high pitch, spiral, male thread comprising a cord. spirally disposed thereon, said tubes being in substantially end to end abutting relationship, and at least one paper sleeve internally threaded with a mating high pitch, spiral, female thread, one of said sleeves being disposed in threaded engagement with and extending across the abutting ends of adjacent tubes, said female thread having at least one of its side edges beveled at an angle of between about 6 and 30 to receive the male thread in locking relationship when tensile stress occurs between tubes and sleeve.

7. An assembly in accordance with claim 6 in which the tubes and sleeves are substantially the same length.

8. A threaded explosive assembly having in combination a plurality of tubular explosive cartridges, each comprising multi-ply paper shells containing explosive material, said cartridges carrying an external, high pitch, spiral,

male thread consisting of a cellulosic cord disposed beneath at least one outer ply of the shell and being in end to end propagating relationship, and at least one multi-ply paper sleeve carrying a mating internal, high pitch, spiral female thread, said thread consisting of a strip of flat cellulosic material spirally disposed about the inner periphery of the sleeve in spaced relationship, one of said sleeves being disposed in threaded engagement with and extending across each pair of abutting ends of adjacent cartridges, said female thread having at least one of its side edges beveled at an angle of between about 6 and 30 to receive the male thread in locking relationship when tensile stress occurs between cartridges and sleeves.

9. An assembly in accordance with claim 6 in which the cartridges and sleeves are substantially the same length.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,884,973 Hoke Oct. 25, 1932 1,966,520 Rayner July 17, 1934 2,056,112 Pratin Sept. 29, 1936 2,313,861 Caldwell Mar. 16, 1943 2,317,354 Bennett Apr. 27, 1943 2,403,488 Bennett July 9, 1946 2,413,862 Cohan Jan. 7, 1947 2,429,079 Smith Oct. 14 1947 

